1. RRP & PIT Deformation & RRR Comparison: M. Brown, C. Tarantini, W. Starch, W. Oates, P.J. Lee, D.C. Larbalestier ASC – NHMFL – FSU M2OrA – 05 06/30/15

2. Acknowledgements This research was funded by the Department of Energy; Office of High Energy Physics under Grant #: DE-SC0012083 RRP® strand provided under the DOE Conductor Development Program that is managed by D. Dietderich of the Lawrence Berkeley Laboratory. PIT strand was supplied to us by the US LHC Accelerator Research Program (LARP), which is a BNL, FNAL, LBNL, and SLAC collaboration with CERN for the High Luminosity LHC program: http://www.uslarp.org/ 2

3. 3 Experiment What have we done? AA quantitative study of the shape and position of filaments (sub-elements) after rolling lengths of unreacted PIT & RRP® round wires to simulate cabling deformation. RRRR values taken in varying stages of deformation. DDiffusion Barrier leakages quantified and compared to filament distortion. Why? TTo benchmark the deformation to determine a limit past which unacceptable damage has occurred, and for discussion on how to best limit this damage So What? WWe find that a critical distortion occurs for thickness reductions between 10 and 20%. IIn this range, the filament shapes transition from higher aspect ratio in outer filament rings to much larger aspect ratios in inner filament rings, especially in the vicinity of the strong 45˚ shear bands imposed by the rolling CComparison with RRR gives direct performance comparison of deformed strands. 10% TR 0% TR 20% TR 30% TR

4. 4 Previous Work Rolling Experiments to simulate Rutherford cabling: Turrioni D, Barzi E, Bossert M, Kashikhin V V, Kikuchi A, Yamada R, and Zlobin A V 2007 Study of Effects of Deformation in Nb3Sn Multifilamentary Strands IEEE Transactions on Applied Superconductivity 17 2710–3  “A procedure that makes use of both microscopic analysis and macroscopic measurements was established to study effects of deformation in brittle superconducting strands.” Ghosh A K, Cooley L D, Dietderich D R, and Sun L 2008 Transport and Magnetization Properties of Rolled RRP Nb 3 Sn Strands IEEE Transactions on Applied Superconductivity, vol. 18, no. 2, pp. 993–996  Carried out transport, magnetization, and RRR measurements on rolled RRP strands. Showed that RRR is the most greatly affected. Barzi E, Turrioni D, and Zlobin A V 2014 Progress in RRP Strand Studies and Rutherford Cable Development at FNAL IEEE Transactions on Applied Superconductivity 24 1–8  Used flat rolling to test electrical performance of conductors after varying degrees of deformation. In this work, we build upon previously used methods with a targeted focus on the shape change in the individual filaments (PIT) or sub-elements (RRP®). 10% TR 0% TR 20% TR 30% TR

5. 5 Experimental Procedure Strand rolled in ~5% increments Samples taken at 10% increments: 10, 20, & 30% Thickness Reduction (TR) Wires then heat treated:  Treatments in table below Samples then polished and imaged in SEM using Backscatter detector RRP 108/127 Manufacturer: OST Supplier: DOE /CDP WIRE SPECS: PIT 192/217 Manufacturer: Bruker Supplier: DOE /CDP

6. 6 Filament Shape Definition Steps: Isolate DB and Cu interface Threshold between color values Subtract Cu portion to isolate filament shape Use image analysis to compile filament data A B

7. 7 Image Analysis Techniques on Full Strand θ 0˚ 180˚ 90˚ * Every filament isolated * Analysis performed only on top half due to symmetry * Rings labeled 1 through 4 starting on innermost ring* Superimpose radial axis with origin at center of strand * Find each filament’s radial position and the distance from center of the strand

8. 8 PIT – Deformation vs. Angular Position 9045 135 0 Undeformed 0% 9045 135 0 10% No obvious radial trends Slight increase at 90 deg

9. 9 9045 135 0 PIT – Shear Bands of Large Deformation 30% 20% ① ⑦ ① ⑦

10. 10 RRP – Deformation vs. Angular Position No obvious radial trends High AR at Ring 4 hex corners Slight increase in AR at 90° 0% TR 10% TR

11. 11 30% TR RRP Aspect Ratio – Shear Bands at higher TR ① ④ 20% TR ① ④

12. 12 PIT – Inner Filament Deformation Upon Rolling Undeformed 0% ① ② ③ ④ ⑤ ⑥ ⑦ 10% ① ②③ ④ ⑤ ⑥⑦ 20% ① ② ③ ④ ⑤ ⑥ ⑦ 30% ① ② ③ ④ ⑤ ⑥ ⑦ ① ② ③ ④ ⑤ ⑥ ⑦

13. 13 RRP – Inner Filament Deformation Upon Rolling

14. 14 Ring # 0% TR10% TR20% TR30% TR 10113 20013 30031 40022 50002 60321 70110 PIT Damage Trends – DB Leakages Ring # 0% TR10% TR20% TR30% TR 10113 20013 30031 40022 50002 60321 70110 Total051012 # of DB Breakthroughs in Rings Two general trends are seen in both the table and graph. Obvious: breakthroughs increase with increasing thickness reduction Less obvious: Breakthroughs are favored on inner rings as %TR increases *Note: Breakthroughs counted from entire cross-section (not just top half) TRRRR 0%79.90 10%59.06 20%32.95 30%19.36 Diffusion Barrier Sn leakage in 20% TR sample indicated by Kirkendall void, and A15 formation on outer DB

15. 15 RRP Damage Trends - DB Leakages Standard Sn Reduced Sn Diffusion Barrier Sn leakage in 10% TR sample indicated by Kirkendall void, and A15 formation on outer DB Again, two general trends are observed. Obvious: breakthroughs increase with increasing thickness reduction Less obvious: Breakthroughs are favored on inner rings as %TR increases

16. 16 Damage Trends – RRR degradation @ 20% TR Standard Sn Reduced Sn Good ≤ 10%Bad ≥ 20% Reduced Sn has higher values of RRR, however, this value drops significantly between 10 and 20%. Standard Sn values for RRR are mostly preserved from 0 to 10%.

17. 17 DB Leakage - Corner Filaments are not the problem!  Note that it is not the outer corner filaments that are leaking, but the inner filaments.  If Sn leakage is to be affected significantly, support must be given to the inner filaments. 30% TR 20% TR

18. 18 Concluding Remarks – Hex Corner Filaments Total fraction of hex corner filaments leaking  6 per cross section  4 cross sections per sample  4 samples  96 total corner filaments observed  Only 3 leaks from corner filaments  only 3.1% total rate of leakage Inner ring filaments become the most heavily distorted as deformation increases leading to diffusion barrier failure.  Rings 1 and 2 make up 23 filaments in each cross section  4 cross sections per sample  4 samples  368 total filaments observed in Rings 1 and 2  62 leaks from filaments in Rings 1 and 2  16.8 % rate of leakage  All but 3 of these leaks happen after 20% TR for inner rings  DB leakage rates for inner two rings go from 0.8% (@ 10%TR) to 4.3% (@20%TR), then to 16.8% (@30% TR) What does this mean? We should be worried about inner filaments, not hex corners. Q & A